Water shutoff in oil and gas wells



QNITED STATES PATENT OFFICE a229,: WATER snurorr m on. AND GAS WELLS Harvey T. Kennedy, Oakmont, and Abraham J. Tcplitz, Penn Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application May 26, 1939, Serial No. 275,998

This invention or discovery relates to water connate water persists in the pay formations shutoff in oil and gas wells; and it comprises an during flow of oil in the well. A well may be pro- Patented Jan. 21, 1941 I I improvement in methods of shutting off water in ducing oil only, while the oil sand may haveits oil or gas wells by injection of fluid plugging interstices half full of water.

v agents into the well and surrounding water-bear- This wide-spread presence of water in the pay 5 ing and oilor gas-bearing formations, said imformations militates against the success of any provement comprising the steps of injecting into water shutoff method, because of deposition of the formations a fluid substance, advantageously plugging matter in the oil formations. Shutofi one of water-soluble nature, and of such chartreatments with selective agents (inert to oil) 10 acter as to delay or prevent formation of a plug injected indiscriminately as described are large- 10 by the plugging agent, and then releasing pres- 1y successful, provided the pay formations consure on the well to cause said fluid substance to tain only a little water. They plug the wet sands. be flushed out of the water-bearing formations, and even if they do deposit some sealing material while leaving some of said substance in the pores .in the pay formations, the net ratio of oil to waof the oilor gas-bearing formation, and then ter produced from the well is increased. How- 15 injecting said plugging agent, whereby plugging ever, with high concentrations of connate water of the water-bearing formation is assured, while in the oil sands, the treatment becomes ineffecplugging of the oil-bearing formation is obviated; tive and may even kill the well. all as more fully hereinafter set forth and as There is a desideratum for a process of shutclaimed. ting off water in oil and gas wells containing con- 20 In oil wells, formations producing water or nate water in the pay formations wherein the brine alone are frequently encountered closely plugging agent can be injected indiscriminately adjacent oil or gas producing formations (pay into the water producing formations and the pay formations). It is a desideratum to seal off such formations, but the plugging action of the treatwet formations, to prevent influx of water to the ing agent can be limited to the water producing well. One way of sealing wet formations is to formation, leaving the pay formations unaffected. inject therein a liquid plugging agent, of such In the Kennedy Patent 2,164,459 a method of character as to enter the pores and form a sealhandling this problem is set forth, wherein the ing plug therein. It is of course undesirable that residual connate water in an oil producing formaany plugging of the pay formation take place. tion is first emulsified and subsequently flushed 30 Sometimes it is practicable to temporarily close out of the formation, after which there is injected off or isolate the pay formation, prior to such in the formations adjacent the well afluent mateshutofi treatment, as by means of a packer, but rial inert to oil, but adapted to form a plug in the sometimes this is quite impossible. Where isolapresenceofwater. Sucha method is generally sat- 5 tion of the pay formation is not feasible, a plugisfactory, particularly when the pore spaces in ging agent is selected of such character as to be the formations to be treated are relatively large.

inert to oilto give as little plugging as possible However, it sometimes takes more than one prein the pay formation, and it is injected indiscrimim nary t eat e t in O de to emulsiiy and inately into all the formations; i. e. a batch is move all the water present in the pay formation.

40 simply pumped down the well. when it is possl- Furthermore, when the formations are of low 40 ble to pack off the pay formation as described, permeability it is sometimes difficult to effect the non-selective treatment agents, such as solutions desired emulsification and the removal of the of neutral precipitants injected one after the residual connate water. The process further inother (e. g. calcium chloride solution followed by volves the use of plugging agents having a selecsodium silicate solution) can be employed. This tive action, otherwise the pay formations may be 45 has not been feasible when it is impossible to sealed. temporarily close ofithepay formation. In the present invention we have provided a In methods wherein the shutoff agent is innovel process of selectively shutting oif water in jected indiscriminately, good results have been oil and gas wells containing (or thought to con- I obtained, provided the agent is of such character tain) connate water in the pay formations, 50

as to give no precipitate on admixture with oil, wherein the formations adjacent the well bore or the precipitate is soluble in oil, and provided are subjected to one preliminary treatment which the pay formations are substantially free of waeffectively prevents the fluid plugging agent subw ver. most pay formations contain, sequently injected into the well from being transalong with the oil, appreciable amounts of conformed into an obstructing plug, in the pores nate water or brine, in wetting contact with the through which the oil or gas flows to the well rock or sand pores and particles. It appears that ore.

all, or at least most, pay formations contain some According to our invention, we first inject into connate water. Oil-bearing sands and rocks are the formations adjacent the well bore, under pres- Gil 6o preferentially wet by water or brine. and the sure, a preferentially water-soluble fluid sub- 6 y stance of such character as to prevent the plugging agent subsequently to be injected from forming an obstructing plug when in contact with a water solution of said substance. The fluid substance penetrates a substantial distance into both the water producing formations which are ultimately to be sealed off and the pay formations which are to be left unobstructed. The pressure on the well is then released to cause .the well to flow. This takes place naturally if the formation pressure is the formation pressure is low, the well may be pumped to cause the well fluids to flow toward the well from both water-producing and oil-producing formations. The well is permitted to flow sufficiently to remove all of the fluid substance which has found its way into the water-producing formations.

At this stage of the operations, that portion of the fluid substance which originally entered the water-producing formation or formations has been flushed therefrom by the now. But that portion which has been forcedinto the oil-producing formations, being preferentially watersoluble, has dissolved in the connate water therein and remains on the surface of the rock particles or sand in the formation. It is not removed by the passage released and the well permitted to flow. The connate water associated with the oil producing formations is thereby converted into a solution which prevents the'transformation of the fluid plugging agent into an obstructing plug in the oil-carrying passages.

Subsequently, there is introduced into the well and injected into the formations adjacent thereto a fluid plugging agent adapted to form an obstructing material when not in contact with the inhibiting substance previously iniected. This plugging agent penetrates into both the waterproducing and oil-producing formations. As the water-producing formations have been flushed free from any inhibiter, the plugging agent ultithese passages. However, that portion of the plugging agent which finds its way into the oil producing formations is prevented from obstructing the oil-carrying passages by the action of the inhibitor mately obstructs that the plug in action of the plugging agent is entirely limited to the water producing formation leaving the pay formations unan'ected and productive.

tion of the plugging agent into an obstructing material or, at least, to so delay the transformation of the fiuid plugging agent that the pluggin material in the water-producing formation is fluid, whereby on releasing the pressure it is flushed out of the oil-bearing passages before any substantial precipitation. or gelation commences. When the substance used in preliminary treatment is of the type which delays, rather than prevents, precipitation of the tive plugging agents place only in those passages from which oil is already obstructed by the presence of connate water held in close amnity to the sand grains.

A variety of substances are used as plugging agents in effecting water shut-off and the-inhibitor used as a preliminary treating substance in our process varies wlththe particular subv stance employed as plugging agent. Some known plugging agents are characterized by their ability to' react with the salts in solution in oil fleld brines to produce plugging precipitate. Other plugging agents are characterized by their ability to be transformed into plugging precipitates or gels when brought into contact with either fresh water or brines. Still other plugging agents are characterized by the fact that they are composed of two mutually-precipitable solutions ordinarily of oil when the pressure is injected into the well in sequence. Other plugging "agents are fluid substances adapted to set or harden with the passage of time without coming in contact with or reacting with other substances. As before stated, the substance employed in preliminary treatment is selected according to the plugging agent we use. For instance, when w the plugging agent to be used is a colloidal suspension such as red liquor (iron oxide sol) which i is broken by the action of salts in solution such as MgC'Iz, NaCl, and CaCh, the substance emv where the brines encountered are concentrated and particularly where they contain appreciable quantities of calcium and magnesium salts we use a substance such as sodium lauryl sulfate which is not precipitated For waters containing only any alkaline buffer may be employed.

When the plugging agent to be subsequently employed is one which hydrolyzes or hardens in the presence of water to form an obstructing plug, the substance employed in preliminary treatment is a substance which will prevent hydrolysis or hardening of the plugging agent or at least delay it for an-appreciable time. For example, one of the most advantageous selecknown is methyl silicate which in practice is often injected into the well in combination with an accelerator to decrease the setting time of the mixture on coming into contact with water. Such procedure is described in the copending application of H. T. Kennedy, Serial No. 137,585, filed April 17, 1937. Thus, a mixture of 50 volumes of methyl silicateacsodium salts, almost 7 a temperature of 140 F. In using such a plugging agent we employ as a preary treating substance one of various substances which delays the setting time of the by alkaline earth salts.

nium oxalate, a

diethanolamine,

We have found that ammodrazine will appreciably retard of the organic silicates when brine in which the preliminary phenylhysetting time contact with treating sub-'- stance is dissolved. Likewise, the organic oxygen-containing s cohols, glycols, in water than olvents (e. g. acetone, etc.) which are more in oil are useful as treating substances lower alsoluble preliminary tion wlthfthe organic nitrogen-containing compounds y before mentioned. They also delay gelatior'ii' The .Jeffect of the prelim setting time cent by weight inary treating subf methyl silicate tables below. The setting time of 50 cc. methyl silicate containing 0.95 per hydrochloric acid idify at a temperature of 140 and 15 cc. of

F. Table I illustrates the effect on the setting time of certain organic nitrogen-containing compounds.

TABLE I Preliminary treating g ia ak substanoe the water ours M.-

I Percent None l. 2 1. 0 Ammonium oxalate 0. 6 l. 0 i. 3

l. 0 2. 3 l. 9 Aminoecetic acid 0. 5 3. 1 2. 6

1. 0 3. 6 3. 0 Phenylglycine 5. 0 2. 5 2. 1 Diethanolamine 0. 25 2. 0 l. 'I

The ratio of the normal setting time can be by introducing the nitrogen co retarded setting time to the further increased ntaining compound in solution in an organic oxygen-containing solvent such as acetone, In such instances by reaction ethyl alcohol or both the nitrogen compound ate, either s of the well brine or ponent subsethe like.

and the solvent are eilfective in retarding the setting time as illustrated by Table 11 wherein 50 cc. of methyl silicate is added to 15 cc. of treated brine:

TABLE II Composition 0! solution Setting Retarded setting time to which methyl silltime, Ratio cats is added hours Normal time 1.0% phenylglycine in 60-40 brine-acetone sol 6.5 5.4 3.0% phenylglycino in 60-40 brine-acetone sol 9.3 7.8 5.0% phenylglycine in 60-40 brine-acetone sol 10.3 as 1.0% o-aminophenol in 60-40 brine-acetone sol 5.0 4.2 1.0% phenyihydrazine in 60-40 brine-acetone sol 0.6 8.0 0.5% phenyihydrazlne in 60-40 brine-methyl alcohol 7.5 6.3 60% brine-40% acetone- 3. 5 2. 9 607 brin hyl cohol 2.4 2.0 00% brine-40% methyl alcohol 2.3 1.9

used is of such by metathesis into by reaction action product,

- cent the bottom quently introduced, the effectiveness of the plug is dependent on the size of the insoluble crystals formed. found that in such cases itis advantageous preliminary treating agent aprotective colloid such as gelatin or various of the water-soluble gums, which although allowing metathesis and precipitation oi the rethe growth ofcrystals to such an extent that obstruction to flow does not result and the fine precipitate is easily flushed from the oil-bearing passages when the pressure is released. Such protective colloids are also effective preliminary treating agents in those processes wherein the plugging agent employed in a colloidal suspension such as an iron oxide sol which is transformed into a flocculent precipitate by the action of the salts in the well brines or by the action of electrolytes subsequently injected for the purpose of breaking the sol. The precipitate produced in the presence of a protective colloid is non-flocculent, very fine, and will not plug the oil passages.

The following examples, showing'various specific embodiments of the invention, serve to illusltetarded setting time Normal setting time trate the manner in which the invention is carried out in practice.

Example I In treating a flowing well making both oil and water and having the usual casing and tubing, a preliminary treating substance is prepared by dissolving 87.5 pounds of phenylglycine in 5 barsolution is well, the casting head being open. The'casing head is then closed and the preliminary treating substance is forced into the formations adjaof the well by loading the tubsuch specific gravity as to float such pressure as is necsubstantial dising with oil (of on the solution) under 'essary to inject the charge a tance back from the well bore. At such time as it is estimated the preliminary treating substance has traveled into the adjacent formations for a considerable distance the injection is stopped, but the pressure is maintained to prevent the well iromflowing for, say, one-half hour. The pressure is then released and the well produced through the tubing for suflicient time to insure that the preliminary treating substance has been entirely flushed out from any water-producing formations. The casing head is again opened and there is then pumped down the tubing to the bottom of the well under a head ofoil, two barrels of a iiuid plugging agent consisting of methyl silicate having incorporated therewith 0.95 per cent 'by weight hydrochloric acid to adjust the setting time of the plugging 1.2 hours under normal conditions. The casing head is again closed and the silicate plugging agent is injected into the formation for a substantial distance away from the well bore by loading the tubing with oil under pressure and the about 8 hours so that the plugging agent will set in the water producing formations. At the coming to the same endcf this time any plugging agent in the pay formations, being In a pumping well, the well .is pumped to lower the fluid level as far as possible. According to acid to the mixture. Usually the acid is added to the water prior to mixing, as the operation is thereby facilitated and the mixture made more uniform. This fluid plugging agent is injected into the formations adjacent the well bore, acmechanical procedure employed in injecting the preliminary treating sub. stance. The well is again closed in for about 10 hours, after which the pressure is relieved and the well again produced slowly by pumping.

Example III This example illustrates one specific embodiment of the invention accomplished by injecting in sequence two solutions normally adapted to. cipltate by metathesis.

In treating a producing well, the conditions being those encountered in Example I, a batch tion of 'gum arabic (5%) or gelatin (1%) is pumped down the tubing to the bottom of the well, is forced into the formation adjacent thereleased and-the well produced suiliciently to insure 'adequate flushing out of the preliminary treating substance from the water producing well is again closed in for 1n colloidal formation. Any excess of water. and colloidal sol that is not held in ailinity by the connate water originally present will be flushed out of the pay formation, but enough protective colloid remains quently we'inject, in sequence, a pair of mutually precipitable solutions such as an aqueous solution of sodim carbonate or bicarbonate (say, a A

released and The gelatin or gum arabic which has been retained in colloidal soluout of the pay formation. However in the water producing formations there is nothing to retion (prepared from 40.5 Bpsodium silicate 3.22 SiOz:1 NazO) of specific gravity 1.115. In mixing these constituents the silicate should be added to the acid with constant stirring. Prepared in this way, the mixture fluid sol whichhas a setting the aid of an oil load, and the well is shut in for about 2% hours to allow the plugging agent to set in the water formation. The

as little as possible.

Prior to our invention, in order to prevent the obstruction of pay formations it was necessaryto The foregoing examples are cited by way of illustration only. The method described is susing solvent and said plugging agent is a fluid ceptible of numerous variations without departsilicate sol. ing from the spirit and scope of the invention as 3. A process of selectively shutting off aqueous defined in the appended claims. liquids in oil and gas wells which comprises in- In the specification and claims the term plugdiscriminately injecting into both pay forma- 5 ging agent is employed to indicate any fluid subtions and aqueous liquid producing formationsstance which undergoes transformation to form under pressure a preliminary treating substance an obstructing plug in the formations. Where comprising an acetone solution ofan amino commore than one fluid substance is injected to propound substantially more soluble in water than duce a plug, 1. e. where the plugging agent is in oil, releasing the pressure and causing the well divided into two components, the term plugging to flow sufiiciently to remove said preliminary agent is used collectively. The term preliminary treating substance from any aqueous liquid protreating substance is employed to indicate those ducing formation, subsequently indiscriminately fluid substances which delay or prevent the transinjecting into said formations under pressure a formation of a plugging agent when in contact fluid plugging agent comprising an organic silil5 therewith. cate adapted to form an obstructing plug on con- What we claim is: tact with the aqueous liquids in the formation 1. A process of hutting off aqueous liquids in and adjusted with acid to normally form a sealoil and gas wells which comprises injecting under ing plug comprising hydrated silica in contact pressure into both pay formations and aqueous with an excess of the aqueous hquid at a sub-, liquid producing forma ions adjacent awell bore stantially definite time after coming in contact a fluid preliminary treating substance more soltherewith, maintaining the pressure on said pluguble in water than in oil and comprising an inging agent for a time approximately correspondhibitor adapted to at least delay transformation ing to the normal setting time and thereafter of a subsequently injected plugging agent into an releasing the pressure and causing the well to 2 obstructing plug when in contact therewith, reflow sufficiently to remove unset treating agent leasing the pressure and causing the well to flow from the formations. sufficiently to remove said preliminary treating 4. A process according to claim 1 wherein said substance from any aqueous liquid producing preliminary treating substance is an acetone soformation, subsequently injecting into both said lution of phenyl glycine and said plugging agent formations under pressure a fluid plugging agent is an alkyl ester of orthosilicic acid. transformation of which into an obstructing plug 5. A process according to claim 1 wherein said is delayed by contact with said inhibitor, mainpreliminary treating substance is an alkaline taining pressure on the well to prevent flow for buffer solution and said plugging agent is a cola time sufficient to enable transformation of unloidal suspension of such character as to be norinhibited plugging agent into an obstructing plug, mally broken by the action of well brines with but insuficient to permit transformation of any production of an insoluble obstructing plug. plugging agent in contact with said inhibitor and 6. A process according to claim 1 wherein said thereafter releasing the pressure and causing the preliminary treating substance is a protective well to flow sufficiently to remove untransformed colloid and said plugging agent comprises a sub- 40 plugging agent from said formations. stance adapted to be transformed by metathesis 2. A process according to claim 1 wherein said into a crystalline water insoluble precipitate. preliminary treating substance is an amino com- HAR pound in solution in an organic oxygen-contain- ABRAHAM J. TEPLITZ. 

